Inside Demi Moore's Dangerous Desperation to 'Stay Young and Skinny'

Never shy about flaunting her bikini body onscreen and off, Demi Moore had long been regarded as Hollywood's most age-defying beauty.

But as the actress approaches her 50th birthday – and her marriage to Ashton Kutcher, 33, began to crumble – several sources tell PEOPLE in this week's cover story that the 49-year-old star battled deep feelings of insecurity. In fact, sources say the star was barely eating and partying wildly before her drug-fueled breakdown.

"As Demi got older, she convinced herself that she needed to stay young and skinny to remain attractive to her husband," says a source who knows the former couple.

Continues the source: "She needed reassurance all the time that she was hot and sexy."